1. Field of Invention
The present invention relates to an inspection device for detecting drugs and explosives utilizing the ion mobility technique, in the security detection field, and in particular to an ion mobility spectrometer (IMS) capable of effectively promoting sample injection efficiency.
2. Description of Prior Art
The ion mobility spectrometer (IMS) effect identifies ions based on different drifting speeds of different ions in a uniform weak electric field, and is generally constituted by a sample injection section, an ionization section, an ion gate, a drift region, a collection region, a reading circuit, a data collection and process section, and a control section and the like.
In the prior art, a semipermeable membrane is employed so that it makes the environment cleanliness level required by the IMS lower. A negative pressure is formed by designing and adjusting appropriate air flow speeds on both sides of the semipermeable membrane, however, the effect of the negative pressure is limited to a certain degree and thus the sample injection efficiency remains low.
Chinese patent document CN1916619A discloses an ion mobility spectrometer based on sample injection of a membrane, which utilizes a micro-pump coupled in series between the semipermeable membrane and the ionization region to form negative pressure, increasing the permeation rate of the semipermeable membrane. However, since the micro-pump is coupled in series in the system, and most drugs and explosives as well as the semipermeable membrane per se need work at the temperature above 100 degrees, such as 180 degrees, which is high for the micro-pump that cannot run continuously and steadily at the high temperature, the application and the service life of the IMS are limited to a certain degree. Moreover, the interior structure of the micro-pump is easily polluted and difficult to clean, resulting in performance degradation of the IMS.
Referring to FIG. 1, another structure employed in the prior art includes a sample injector 1, a semipermeable membrane 2, an ion source 3, an ion gate 4, a ring electrode 5, and a Faraday plate 6 which are arranged along a drift tube in turn, and further includes an air extracting pump 10 connected with an opening 9, a filtering device 12 connected with an opening 11, and a filtering device 8 connected with an opening 7. The ambient air flows through the filtering device 12 and then enters the ionization region through an aperture 13 near the semipermeable membrane 2, and forms high-speed air flow near the semipermeable membrane 2 so as to form such an air pressure difference between the opposite sides of the semipermeable membrane 2 that the molecules to be detected will be introduced. The migrant air enters the drift region through the filtering device 8, and is extracted out of the drift tube along with the reaction air through the pump 10. The problem in the above described prior art is that a controllable low air pressure is formed at the side of the semipermeable membrane which causes the sample injection efficiency of the semipermeable membrane to be reduced.